This invention relates to improvements in an x-ray spot film device which is used in conjunction with an x-ray table to make a selected number of radiographic exposures on a single film and to perform fluoroscopic examinations.
Conventional spot film devices usually comprise a support or frame extending crosswise over the top of an x-ray table. A main carriage is mounted on the support for being advanced from a rearward parked postion to a frontward radiographic position wherein a cassette carried by the carriage is disposed in alignment with an x-ray beam that is projected through a patient from an x-ray source in the table. The cassette is mounted in a tray supported on an inner carriage which is translatable crosswise of the main carriage so that the center of the x-ray beam may be made coincident with the area on the film cassette on which a spot film exposure is desired. The area is further defined by superimposable masks.
As is well known, spot film devices are also provided with a fluoroscopic device which permits an examining radiologist to visualize anatomy of interest and to make one or more radiographs in a choice of sizes by projecting the cassette forward and shifting it and the masks to obtain the desired sequence of radiographs. The fluoroscopic device on the spot film device is aligned with the x-ray source in the table, and the film cassette is, of course, retracted from the beam during fluoroscopy.
When a fluoroscopic view of interest is observed, the film cassette must be projected into the x-ray beam path rapidly and one or more exposures must be taken while the fluoroscopically observed condition persists. In prior art spot film device, the main carriage which supports the inner carriage on which the film cassette is mounted is usually driven rearwardly to parked position with a unidirectional motor that moves it slowly and loads a return spring at the same time. The carriage is latched in parked position and when the latch is released the carriage is advanced rapidly under the influence of the spring and halted abruptly in the radiographic position. Rapid movement ad abrupt halt of the carriage and the masks results in considerable noise, shock and vibration that necessitate use of shock absorbing devices such as dash pots to reduce these ill effects. One problem with this system is that the main carriage must be restored to a rearward position after each exposure, to reload the spring, after which the carriage must be projected forwardly again to make the next exposure.
Some prior spot film devices have a set of tracks for the main carriage. After each exposure, the carriage is returned rearwardly and shifted to different tracks, similar to railrod car switching. Then the carriage is driven forwardly and it arrives in the proper position for the next exposure to be made. This is a relatively slow method and it requires a larger and complicated mechanism which has many moving parts.
In prior art spot film devices two x-ray field defining masks having elongated rectangular apertures disposed at right angles to each other are used. One of the masks is moved manually into the x-ray beam when two adjacent cross-wise exposures are to be made on the film. The other mask is usually carried on the palpator cone device so it and the palpator cone are disposed in the beam when two adjacent exposures lengthwise of the film are desired. Both masks and the cone are in the beam when quadrants or four exposures on one film are desired. Manual movement of the masks, in accordance with the prior art, is distracting to the radiologist and it tends to slow down the procedure undesirably.
Some prior art spot film devices dispose an x-ray anti-scatter grid permanently in the x-ray beam path. As is well known, a grid is comprised of a large number of lead strips disposed edgewise of the x-ray beam and in parallelism with each other or at predetermined angles in focused grids. A grid permits passage of x-rays which emanate from the focal spot of the source in a direct or straight line to the radiographic film or fluoroscopic device. Rays which are scattered by the equipment and by the intervening body being examined are intercepted by the lead strips and are largely prevented from reaching the film or fluoroscopic device where they may cause undesirable fogging of the image and poor sharpness.
Fluoroscopic procedures are preferably conducted with a low ratio grid or no grid. Radiographic procedures, on the other hand, are preferably conducted with a high ratio grid. In prior art apparatus where only one grid is available, a low ratio grid is usually installed since it can be used for fluoroscopy and radiography even though sharpness of the film image is not as good as it would be if a high ratio grid were used for radiography. The high ratio grid cannot be the sole grid used for radiography and fluoroscopy since it would reduce image intensity or brightness too much for fluoroscopy.
Another component of a spot film device to which consideration will be given is the palpator. The palpator comprises an x-ray permeable cone which may be advanced into the x-ray beam path during fluoroscopy. The cone may be brought down by moving the whole spot film device downwardly, to depress the patient so that the movements of an x-ray opaque material which may have been ingested by the patient can be visualized on the fluoroscopic device. On some occasions, the radiologist moves the spot film device laterally or frontwardly and rearwardly while the cone is impressed in the patient's body. This requires the radiologist, after having moved the cone carriage forwardly as in prior art spot film devices, to lock the cone so it will not slip on the spot film device while the device is being manually oscillated to effect palpation. The need for the radiologist to devote attention to moving the palpator manually and to locking and unlocking it is also distracting and slows down the procedure.